Add firewall content

content/roadmaps/102-devops/content/104-setting-up-x/104-firewall.md

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-# Firewall
+# Firewall
+
+Firewall is a **network security device** that monitors and filters incoming and outgoing network traffic based on an organization’s previously established security policies. It is a barrier that sits between a private internal network and the public Internet. A firewall’s main purpose is to allow non-threatening traffic in and to keep dangerous traffic out.
+
+<ResourceGroupTitle>Free Content</ResourceGroupTitle>
+<BadgeLink colorScheme='yellow' badgeText='Read' href='https://www.checkpoint.com/cyber-hub/network-security/what-is-firewall/'>What is Firewall?</BadgeLink>
+<BadgeLink colorScheme='yellow' badgeText='Read' href='https://www.cisco.com/c/en_in/products/security/firewalls/what-is-a-firewall.html'>Types of Firewall</BadgeLink>